Gps with aiding from ad-hoc peer-to-peer bluetooth networks

ABSTRACT

The present invention is related to location positioning systems, and more particularly, to a method and apparatus for providing an update of ephemeris information. According to one aspect, GPS enabled devices in the signal unavailable area monitors the state of its ephemeris data and time information. When the ephemeris data and time information become out of date, the GPS enable device uses an ad hoc Bluetooth network to retrieve ephemeris data and time information from another GPS enabled device with more current data. According to further aspects, a map of a deep hole region in which GPS and other cellular signals are not available, is generated to enable power reduction and cost saving measures.

FIELD OF THE INVENTION

The present invention is related to location positioning systems, andmore particularly, to a method for providing updated navigational datavia a short range wireless network.

BACKGROUND OF THE INVENTION

With the development of radio and space technologies, several satellitesbased navigation systems (i.e. satellite positioning system or “SPS”)have already been built and more will be in use in the near future. SPSreceivers, such as, for example, receivers using the Global PositioningSystem (“GPS”), also known as NAVSTAR, have become commonplace. Otherexamples of SPS systems include but are not limited to the United States(“U.S.”) Navy Navigation Satellite System (“NNSS”) (also known asTRANSIT), LORAN, Shoran, Decca, TACAN, NAVSTAR, the Russian counterpartto NAVSTAR known as the Global Navigation Satellite System (“GLONASS”)and any future Western European SPS such as the proposed “Galileo”program. As an example, the U.S. NAVSTAR GPS system is described in GPSTheory and Practice, Fifth ed., revised edition by Hofmann-Wellenhof,Lichtenegger and Collins, Springer-Verlag Wien NewYork, 2001, which isfully incorporated herein by reference.

The U.S. GPS system was built and is operated by the United StatesDepartment of Defense. The system uses twenty-four or more satellitesorbiting the earth at an altitude of about 11,000 miles with a period ofabout twelve hours. These satellites are placed in six different orbitssuch that at any time a minimum of six satellites are visible at anylocation on the surface of the earth except in the polar region. Eachsatellite transmits a time and position signal referenced to an atomicclock. A typical GPS receiver locks onto this signal and extracts thedata contained in it. Using signals from a sufficient number ofsatellites, a GPS receiver can calculate its position, velocity,altitude, and time.

A GPS receiver typically has to acquire and lock onto at least foursatellite signals in order to derive the position and time. Usually, aGPS receiver has many parallel channels with each channel receivingsignals from one visible GPS satellite. The acquisition of the satellitesignals involves a two-dimensional search of carrier frequency and thepseudo-random number (PRN) code phase. Each satellite transmits signalsusing a unique 1023-chip long PRN code, which repeats every millisecond.The receiver locally generates a replica carrier to wipe off residuecarrier frequency and a replica PRN code sequence to correlate with thedigitized received satellite signal sequence. During the acquisitionstage, the code phase search step is a half-chip for most navigationalsatellite signal receivers. Thus the full search range of code phaseincludes 2046 candidate code phases spaced by a half-chip interval. Thecarrier frequency search range depends upon the Doppler frequency due torelative motion between the satellite and the receiver. Additionalfrequency variation may result from local oscillator instability.

The signals from the navigational satellites are modulated withnavigational data at 50 bits/second (i.e., 1 bit/20 msec). Thisnavigational data consists of ephemeris, almanac, time information,clock and other correction coefficients. This data stream is formattedas sub-frames, frames and super-frames. A sub-frame consists of 300 bitsof data and is transmitted for 6 seconds. In this sub-frame a group of30 bits forms a word with the last six bits being the parity check bits.As a result, a sub-frame consists of 10 words. A frame of data consistsof five sub-frames transmitted over 30 seconds. A super-frame consistsof 25 frames sequentially transmitted over 12.5 minutes.

The first word of a sub-frame is always the same and is known as TLMword and first eight bits of this TLM word are preamble bits used forframe synchronization. A Barker sequence is used as the preamble becauseof its excellent correlation properties. The other bits of this firstword contain telemetry bits and are not used in the positioncomputation. The second word of any frame is the HOW (Hand Over Word)word and consists of TOW (Time Of Week), sub-frame ID, synchronizationflag and parity with the last two bits of parity always being ‘0’s.These two ‘0’s help in identifying the correct polarity of thenavigation data bits. The words 3 to 10 of the first sub-frame containsclock correction coefficients and satellite quality indicators. The 3 to10 words of the sub-frames 2 and 3 contain ephemeris. These ephemerisare used to precisely determine the position of the GPS satellites.These ephemeris are uploaded every two hours and are valid for fourhours to six hours. The 3 to 10 words of the sub-frame 4 containionosphere and UTC time corrections and almanac of satellites 25 to 32.These almanacs are similar to the ephemeris but give a less accurateposition of the satellites and are valid for six days. The 3 to 10 wordsof the sub-frame 5 contain only the almanacs of different satellites indifferent frames. The super frame contains twenty five consecutiveframes. While the contents of the sub-frames 1, 2 and 3 repeat in everyframe of a superframe except the TOW and occasional change of ephemerisevery two hours. Thus the ephemeris of a particular signal from asatellite contains only the ephemeris of that satellite repeating inevery sub-frame. However, almanacs of different satellites are broadcastin-turn in different frames of the navigation data signal of a givensatellite. Thus the 25 frames transmit the almanac of all the 24satellites in the sub-frame 5. Any additional spare satellite almanac isincluded in the sub-frame 4.

The almanac and ephemeris are used in the computation of the position ofthe satellites at a given time. The almanacs are valid for a longerperiod of six days but provide a less accurate satellite position andDoppler compared to ephemeris. Therefore, almanacs are not used when afast position fix is required. On the other hand, the accuracy of thecomputed receiver position depends upon the accuracy of the satellitepositions which in-turn depends upon the age of the ephemeris. The useof current ephemeris results in better and faster position estimationthan one based on non-current or obsolete ephemeris. Therefore, it isnecessary to use current ephemeris to get a fast receiver position fix.

A GPS receiver may acquire the signals and estimate the positiondepending upon the already available information. In the ‘hot start’mode the receiver has current ephemeris and the position and time areknown. In another mode known as ‘warm start’ the receiver hasnon-current ephemeris but the initial position and time are known asaccurately as in the case of previous ‘hot start’. In the third mode,known as ‘cold start’, the receiver has no knowledge of position, timeor ephemeris. As expected the ‘hot start’ mode results in lowTime-To-First-Fix (TTFF) while the ‘warm start’ mode which hasnon-current ephemeris may use that ephemeris or the almanac resulting inlonger TTFF due to the less accurate Doppler estimation and ephemerisdownloading. The ‘cold start’ takes still more time for the firstposition fix as there is no data available to aid signal acquisition andposition fix.

Therefore, it is necessary to keep the ephemeris in the receiver currentfor a fast TTFF. Current ephemeris also helps when the received signalis weak and the ephemeris can not be downloaded. Some issued patentsteach receiving the ephemeris through an aiding network or remote serverinstead of from an orbiting satellite. However, this approach results inhigher cost and requires additional infrastructure. Another approach tokeeping ephemeris current, without using a remote server, is toautomatically download it from satellites in the background, such asdescribed in U.S. Pat. No. 7,435,357.

Some commercially available products such as SiRF InstantFixII from SiRFTechnologies of San Jose, Calif. use extended ephemeris to improvestart-up times without requiring network connectivity. With oneobservation of each satellite, SiRFInstantFixII accurately predictssatellite positions for up to three days—removing the need to downloadsatellite ephemeris data at subsequent start-ups—resulting in fullnavigation in as little as five seconds, and with routine 7 meteraccuracy. Moreover, such extended ephemeris products not only starttracking satellites and navigating more quickly, they can do it usingsignals much weaker than those needed to obtain satellite location datathe traditional way, removing the barrier that often blocks successfulnavigation under tough GPS signal conditions.

When a GPS signal is not available and a cellular signal is available,others have used the cellular signal to update the ephemeris data andtime information. However, this method leads to additional cellular overthe air charges.

Nevertheless, some challenges remain. For example, when the receiver isin a location in which satellite signal is not available such as largeoffice buildings, subways, indoor malls, expo halls, etc., the GPSreceiver's stored ephemeris data and time may become out-of-date.Without any GPS signal, cellular signal or other supplementary externaldata source, the tracker cannot determine when to start looking for SVor cellular signal. Under these circumstances the battery for the GPSreceiver can quickly be run down by repeated unsuccessful attempts toupdate the ephemeris and time data.

SUMMARY OF THE INVENTION

The present invention is related to location positioning systems, andmore particularly, to a method for updating ephemeris information of aGPS enabled mobile device in an area in which GPS signal is unavailable.According to one aspect, GPS enabled devices in the signal unavailablearea monitors the state of its ephemeris data and time information. Whenthe ephemeris data and time information become out of date, the GPSenable device (starving device) uses an ad hoc Bluetooth network toretrieve ephemeris data and time information from another GPS enableddevice (donor device) with more current data.

According to another aspect, the GPS enabled mobile device monitors thesignal strength for GNSS, cellular and Wi-Fi. When the respective signallevels drop below a threshold value, a last known position isidentified. When the signal strength is again above the threshold valuethe first fix is identified. The last known position and first fixlocation are uploaded to a server along with the respective timestamps.This information is then used to generate a signal unavailability or“deep hole” map. The deep hole map may be used to evaluate thefeasibility of peer to peer (P2P) ad-hoc networks setup.

According to yet another aspect, the invention utilizes the deep holemap data such that when a device is nearing a deep hole area, the GPSenabled mobile device initiates an update of its ephemeris data toreduce the likelihood of the ephemeris data becoming out of date.

In furtherance of the above and other aspects, a method for updatingephemeris information according to embodiments of the invention includesestablishing a short range wireless connection with at least one othermobile GPS enabled device; and receiving updated navigational data fromthe at least one other mobile GPS enabled device.

In additional furtherance of the above and other aspects, a method forgenerating a deep hole map according to embodiments of the inventionincludes detecting the signal strength of the mobile GPS enabled device;comparing the detected signal strength to a signal strength threshold;determining a last known position location when the signal strengthfalls below the signal strength threshold; determining a first fixposition when the signal strength returns to above the signal strengththreshold; transmitting the last known position data and the first fixposition data to a crowded source server; and utilizing the last knowposition data and the first fix position data to produce the deep holemap.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 is a block diagram of an example implementation of principles ofthe invention;

FIG. 2 is a block diagram illustrating a mobile GPS device according toan embodiment of the present invention;

FIG. 3 is a flow diagram which illustrates a method for updatingnavigational data according to an embodiment of the present invention;

FIG. 4, illustrates a system utilizing a plurality of GPS devicesaccording to an embodiment of the present invention;

FIG. 5 illustrates a method for generating a map of deep holes accordingto an embodiment of the present invention; and

FIG. 6 is a flow diagram illustrating a method of refreshingnavigational data according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe drawings, which are provided as illustrative examples of theinvention so as to enable those skilled in the art to practice theinvention. Notably, the figures and examples below are not meant tolimit the scope of the present invention to a single embodiment, butother embodiments are possible by way of interchange of some or all ofthe described or illustrated elements. Moreover, where certain elementsof the present invention can be partially or fully implemented usingknown components, only those portions of such known components that arenecessary for an understanding of the present invention will bedescribed, and detailed descriptions of other portions of such knowncomponents will be omitted so as not to obscure the invention.Embodiments described as being implemented in software should not belimited thereto, but can include embodiments implemented in hardware, orcombinations of software and hardware, and vice-versa, as will beapparent to those skilled in the art, unless otherwise specified herein.In the present specification, an embodiment showing a singular componentshould not be considered limiting; rather, the invention is intended toencompass other embodiments including a plurality of the same component,and vice-versa, unless explicitly stated otherwise herein. Moreover,applicants do not intend for any term in the specification or claims tobe ascribed an uncommon or special meaning unless explicitly set forthas such. Further, the present invention encompasses present and futureknown equivalents to the known components referred to herein by way ofillustration.

FIG. 1 is a block diagram of an example system 100 for providing updatednavigational data to a mobile GPS enabled device 120. The system 100includes a mobile communications network 102 and a GPS system 104. Themobile communications network 102 provides telecommunications servicesto a mobile GPS enabled device 120. The GPS system 104 includes aplurality of satellites 114, 116, which provide positioning data to theGPS receiver 150 of the mobile GPS enabled device 120. The GPS receiver150 in the system 100 in FIG. 1 may be implemented in a location-basedsystem 110, which is a GPS-enabled device that includes a location-basedapplication 170.

The mobile communications network 102 may be any telecommunicationsnetwork that provides any type of wireless service. A cellulartelecommunications network is one example of such a network. Morespecific examples of such networks include mobile telecommunicationsnetworks based on GSM, CDMA, TDMA, and other signaling protocols.

The mobile communications network 102 communicates with the mobile GPSenabled device 120 using the network's signaling protocol over acommunication link 103. The mobile GPS enabled device 120 includesnavigational data such as ephemeris and almanac data and timeinformation that is periodically updated. In one example, the mobile GPSenabled device 120 may include its own resident GPS receiver and asystem for aiding the GPS receiver by providing updated time andposition information.

The mobile GPS enabled device 120 may also communicate over a secondnetwork, such as a short-range wireless network 106 over a wirelesscommunication link 105. For purposes of this specification, ashort-range wireless network 106 may include any wireless network (evena node-to-node, or peer-to-peer connection) and specifically includespersonal area networks, such as those based on the Bluetooth™ standard.The short-range wireless network 106 may also include wirelessconnections based on other wireless technologies, such as infra-red. Theshort-range wireless network 106 includes a synchronized clock systemthat enables each node connected to the short-range wireless network 106to include a network clock that is synchronized with every other node inthe short-range wireless network 106. In one example, the short-rangewireless network 106 is a Bluetooth™ Piconet™ where the mobile GPSenabled device 120 is the Master Bluetooth™ node and the location-baseddevice 110 is the Slave Bluetooth™ node. Embodiments described hereinare described in the context of using the Bluetooth™ standard whetheremployed in a Bluetooth™ Piconet™ or in a peer-to-peer Bluetooth™connection. Those of ordinary skill in the art will appreciate thatBluetooth™ is referred to herein as an example, and is not intended tolimit the scope of the invention in any way.

Those of ordinary skill in the art will also appreciate that the mobilecommunications network 102 is not to be limited to cellularcommunications networks. Any network that may provide any type ofservice to a mobile handset may be used in alternative examples. Themobile GPS enabled device 120 in the example shown in FIG. 1 is a mobiletelecommunications handset such as a cellular telephone. However, inother examples, the mobile GPS enabled device 120 may be a device forperforming a wide variety of applications over a wireless network (suchas the mobile communications network 102. For example, the mobile GPSenabled device 120 can be a personal navigation device (PND, e.g. fromGarmin, TomTom, etc.), a cell or other type of telephone with built-inGPS functionality, or any GPS device embedded in tracking applications(e.g. automotive tracking from Trimble, package or fleet managementtracking from FedEx, child locator tracking applications etc), or apersonal digital assistant (“PDA”) having a wireless network interface(e.g. as just one example, Wi-Fi capability) in addition to ashort-range wireless network interface.

The location-based system 110 in the example in FIG. 1 may be any systemthat uses GPS services to perform a location-based application 170. Thelocation-based service 110 in FIG. 1 includes a GPS receiver 150 and ashort-range wireless network interface 160. The GPS receiver 150 obtainspositioning data to perform GPS positioning functions via links toseveral GPS satellites 114, 116. The location-based application 110 mayinclude navigation applications such as navigation systems inautomobiles, handheld navigation devices, a PDA with navigation or mapfunctions, or any other application that may operate in a device thatuses GPS services.

Further, GPS Receiver 150 may be implemented using software and/orhardware, including GPS chipsets such as SiRFstarIII GSD3tw or SiRFstarGSC3e from SiRF Technology and BCM4750 from Broadcom Corp., as adaptedand/or supplemented with functionality in accordance with the presentinvention, and described in more detail herein. More particularly, thoseskilled in the art will be able to understand how to implement thepresent invention by adapting and/or supplementing such chipsets and/orsoftware with the frame synchronization techniques of the presentinvention after being taught by the present specification.

FIG. 2 is a block diagram illustrating a mobile GPS device according toan embodiment of the present invention. As shown in FIG. 2, a mobile GPSdevice 120 may include a GPS receiver 150, a Bluetooth unit 214, aprocessor unit 216, and a storage unit 218. The GPS receiver 150 isconfigured to receive navigational data via a satellite signal and toperform positioning functions. The navigational data which may includefor example, ephemeris, almanac, and time information, is stored instorage unit 218 along a timer t_(age). Once the data is stored in thestorage unit, timer t_(ape) is reset to zero and a count initiated viaprocessor unit 216 and used to monitor the time since the previousupdate of the navigational data.

When the timer t_(age) reaches a predetermined count, the navigationaldata may be deemed stale or out-of-date. For example the predeterminedcount may be set to correspond to the time at which a cold start wouldbe required in order to the determine the location of the mobile GPSdevice 200.

The Bluetooth unit 214 may be used to connect to another GPS device toretrieve updated navigational data. In other words, the updatednavigational data for mobile GPS device 120 (starving device) may beobtained by receiving the navigational data (donor device) for the otherGPS device via ad hoc Bluetooth Peer-to-Peer transfer. Given the closeproximity of mobile GPS device 120 to the other GPS device in theno-coverage zone, the navigational data of the other GPS device servesas a good basis for determining the location for mobile GPS device 120.In other words, the accuracy of the transferred assistance data (i.e.,navigational data) will be as good as the size of the no coverage zone.Thus, the navigational data of the other GPS device may be used toquickly determine a first fix position of mobile GPS device 120 uponregaining reception of the GPS signal.

FIG. 3 is a flow diagram which illustrates a method for updatingnavigational data according to an embodiment of the present invention.By way of example, in FIG. 3, the ephemeris and time data are updated.Of course, those of ordinary skill in the art would appreciate that allor any subset of the navigational data could alternatively be updated.At step 310, the signal strength of a mobile GPS device 120 is detected.The monitored signal strength may be any available device communicationsignal, such as GNSS, cellular, and Wi-Fi, for example. If the signalstrength is below a predetermined threshold (e.g., weak signal or nosignal), then at step 320 a search is conducted to determine if there isanother GPS enabled device in peer-to-peer transfer range. For example,the range for communication between two devices via Bluetooth isapproximately 0-300 feet. When another GPS enabled device is located, aconnection is established at step 330. At step 340, a comparison of theage of ephemeris data is made. If the difference in the age of theephemeris data is above a predetermined threshold, then at step 350, theGPS enabled device with the older ephemeris data, receives a transfer ofthe ephemeris data from the GPS enabled device with the more recentephemeris data.

The predetermined threshold value in the difference of the age of theassistance data may be set based on several factors. First, it may beset depending on how the age in the two devices relate to the age valuethreshold, where the age of the ephemeris data would significantlydegrade the time to first fix (TTFF), and the quality of the position(QoP) determination. For example, when such ephemeris age thresholdvalue falls in between the ephemeris age values in the two devices, theephemeris age difference value threshold may be the smallest, i.e., thesensitivity of the need for more up-to-date ephemeris data is thehighest. A small improvement in the age of the ephemeris data of theout-of-date device would make a much more significant contribution tothe improvement in the TTFF and QoP values than in the case where theephemeris data age values in both devices are either significantlyhigher or significantly lower than the critical ephemeris data agethreshold value. For example, if the last valid outdoor acquiredassistance data is becoming out of date after prolonged, two hours longpresence in a no-signal deep hole, twenty minute age difference aroundthis two hours threshold is typically significant enough to initiate thetransfer to refresh the assistance data in the starving data. But thesame twenty minutes age difference is likely to be insufficient if theage of the assistance data is less than forty minutes in both devices ormore than four hours in both devices. Of course, one of ordinary skillin the art would understand that other values could be used for the agedifference threshold for reasons of design preference or to improvepower conservation.

In addition, the predetermined threshold value in the difference of theage of the assistance data may also be set based on the cost ofrefreshing the data in the participating devices and the significance ofthat cost. Such cost factors are mostly related to the loss of power ineither of the two devices. Other factors may include the loss ofcomputational resources such as CPU cycles and memory capacity whenother functions also need to be computed in the devices concurrentlywith the location assistance computations.

Furthermore, similar to refreshing the ephemeris data in the device withmore aged data, the time synchronization assistance data can also beupdated in such device. For this purpose, the devices may compare theage difference between both their ephemeris data and their timesynchronization data.

FIG. 4 illustrates a system utilizing a plurality of GPS devicesaccording to an embodiment of the present invention. For ease ofillustration, in FIG. 4 shows three GPS devices (120A, 120B, and 120C)all of which are configured as shown in FIG. 2. However, one of ordinaryskill in the art would understand that any number of the GPS devicescould also be used. As shown in FIG. 4, the age of the ephemeris data(t_(age)) for mobile GPS device 120B is greater than the age ofephemeris data for mobile GPS device 120A which is greater than the ageof the ephemeris data (t_(age)) for mobile GPS device 120C. Inoperation, assuming GPS devices 120A, 120B, and 120C are all in alocation in which satellite signal is not available, GPS devices 120Aand 120B may each establish a connection with mobile GPS device 120C toretrieve more recent ephemeris and time data. For example, an ad hocBluetooth network connection may be established between the respectiveGPS devices. Of course, one of ordinary skill in the art wouldunderstand that dedicated short-range communications (DSRC) network orother peer-to-peer network configurations (e.g., Wi-Fi) could also beused. Once the transfer of navigational data is complete, the age ofephemeris data (t_(age)) for GPS devices 120A and 1208 may then setmatch that of the ephemeris data for mobile GPS device 120C.

In an embodiment of the present invention, a map may be generated basedon signal strength of mobile GPS device 120. FIG. 5 illustrates a methodfor generating a map of deep holes, in which mobile GPS device 120 isunable to receive a satellite signal. Referring to FIG. 5, at step 510,the signal strength of mobile GPS device 120 is detected. At step 520,the signal strength of the GPS device is then compared to apredetermined threshold value. At step 530, when the signal strength ofmobile GPS device 120 is below the predetermined threshold value, a lastknown position for the device is determined and stored in storage unit207 along with a corresponding time stamp. At step 540, when the signalstrength returns to a value above the predetermined threshold value,such that communication is restored, a first fix position for the deviceis determined and the stored in storage unit 207 along with acorresponding time stamp. At step 550, last known position dataincluding the determined last known position and the corresponding timestamp and first fix position data including the determined first fixposition and corresponding time stamp are transmitted to acrowd-sourcing server. At step 560 a deep hole map is generated usingthe last known position data and the first fix position data. Of course,additional data such as the ephemeris, almanac and other data used todetermine the last known position and the first fix position may also beprovided to the crowd sourcing server.

For greater definition and detail of the deep holes included on the deephole map, a plurality of the GPS devices could be used.

In addition, the generated deep hole map may be updated in real-time.Furthermore, the generated deep hole map may be used to evaluate thefeasibility of ad hoc peer-to-peer network setups.

FIG. 6 is a flow diagram illustrating a method of refreshingnavigational data according to an embodiment of the present invention.Referring to FIG. 6, the method includes generating a deep hole map atstep 610. At step 620, determining a position of the mobile GPS device120 based on the navigational data in the GPS signal. At step 630,determining a proximity to a deep hole based on the determined positionand the generated deep hole map. At step 640, comparing the determineddeep hole proximity to a proximity threshold. The proximity thresholdmay be set according to a last known position used to generate the deephole map, based on a location at a signal strength minimum or mayotherwise be set according to design preference. For example, theproximity threshold may be set to one hundred meter when the device ismoving 120 Km per second speed or 33 meters per second wheremeasurements are taken at a rate of one measurement per second toprovide three reasonable chances to receive the requires location databefore entering the deep hole no signal area.

At step 650, when the mobile GPS device 120 is at a distance from thedefined deep hole less than or equal to the proximity threshold,refreshing the navigational data via the GPS receiver. At step 660,placing the mobile GPS device 120 into a low power or sleep state. Atstep 670, waking up the mobile GPS device 120 at a predetermined timeinterval to check for an available satellite signal using aninfrastructure signal scan. Alternatively, the mobile GPS device 120could also be configured to wake up when a transfer of navigational datais requested by another GPS device, or when the navigational data formobile GPS device 120 becomes stale.

Further, a deep hole device density could also be captured bycrowd-sourcing either as real-time count or as a historical count byTime of Day (TOD) or Time of Year (TOY), etc. and may be used todetermine the wake up time for mobile GPS device 120.

In addition, the method may include power optimization for the donordevices. For example, the donor devices may be configured with a powercharge threshold with respect to is expenditure resulting from donatingassistance data. For ease of illustration, one such example is asfollows. Assume, we have X=600 of starving devices in the hole, and noqualified donor devices around them. Then a number of qualified devicesstart entering the hole, one at a time, with a d=15 min time periodbetween the entrance of each subsequent device. For simplicity, assumeall X starving devices are in DSRC connectivity range with the new donordevice. The new device has good location assistance data, but the powercharge level is so low, that it is sufficient only for P=10 minutes ofDSRC connectivity maintenance, including the connectivity maintenance,S=1 second assistance data exchange with each connected device, thepreceding connection set-up and the follow-up connectivity tear-down forall served connecting starving devices. As soon as this donor deviceenters the hole, connectivity requests from all X=600 starving devicesare queued up in the entering donor device. This could result in asignificant power drain for the donor device as serving all pendingX=600 starving device would have depleted the power charge of the donordevice, since 600*1 sec=10 minutes.

Using the donor device power optimization, the donor device may estimatethe probable outcome of the depletion of its own power charge, knowingthat its own power charge level is enough only for maximum 600assistance data donation sessions and there were already 600 starvingdevices queued up for such assistance donation. In such a case, forexample, the donor device may be configured with the power chargethreshold being set such that no more that 2% or its power charge ondonating assistance data, thus serving only 600*0.02=12 starvingdevices, then rejecting the rest of the queued up requests. Of course,one of ordinary skill in the art would understand that a different valuefor the power charge threshold could be chosen for reasons of designpreference or to improve power optimization. For example, the powercharge threshold could be set to a value corresponding to when the powercharge of the device is sufficient for no more than thirty minutes ofcell phone talk time.

All of the previously starving devices that have received the donatedassistance data may then be utilized as donor devices. In this way, thecomplete process of refreshing the location assistance data for theentire starving device population would also be significantly shortened.Referring to the previous example, the entire process would last 3*12=36seconds only, instead of 600 seconds by “directly recruiting” 12additional donors—i.e., the first 12 served originally starvingdevices—and indirectly recruiting a couple of more devices in the thirdphase through the first generation of recruited donor devices.

Further improvement of the system may be realized by limiting the numberof starving devices for which a connection is accepted (e.g., no morethan 12) and refusing a connection for additional requesting devices,regardless of how many more could be additionally queuing up, by relyingon the already queued up devices as subsequent donor devices. However,after the entering donor device has spent some significant time in thedeep hole, it could potentially become a starving device. Such ambiguitycould be mitigated by knowing a priori what the device density in thehole is and what the anticipated average navigation assistance data agedistribution is in them. Such knowledge can be gained from thecrowd-source server in the infrastructure, as described above. Thehigher the device density, the sooner the entering donor device can cutoff accepting connectivity requests, relying on donor role delegation.At low anticipated device density, there is a reduced likelihood ofcreating a large enough number of donor delegates but the danger of itsown power drain is also reduced. The optimalqueue_size=f(anticipated_starving_device_density) function is thusapproximately a bell-shaped function.

Similarly, the average duration of the devices in the deep hole may alsobe used to determine the threshold: the longer the duration values, themore likely they need refreshments thus increasing the burden on thedonor power charge; but refreshing them would also be more likely toturn them into a qualified donor candidate for other, rejected starvingdevices.

Additional factors which may influence the selection of the refreshqueue cut-off threshold may include the rate of other new donor devicesentering the no-coverage area; and the speed with which the starvingdevices are moving away from their donor device and from the rest of thestarving device population after the receipt of their assistance data.

In an embodiment, mobile GPS device 120 may be further configured todisable the infrastructure signal scan unless other GPS devices in theirimmediate proximity have recently received such infrastructure signalwith acceptable RSS (Received Signal Strength). That is, when the mobileGPS device 120 enters a deep hole region where there are a plurality ofother GPS devices with Bluetooth capability with no recent reception ofinfrastructure signal of acceptable RSS, the periodic infrastructure(i/s) signal scan is disabled such that the mobile GPS device 120 willnot repeatedly attempt to search for a GPS or other cellular signal. Inthis case an ad-hoc connection is established with a plurality of theother GPS devices in peer-to-peer connectivity range in the deep hole totrack time stamps of most recent i/s signal received from theinfrastructure with acceptable RSS. Each of the GPS devices in the deephole stores a timestamp (e.g., last_good_RSS_time value) in its storageunit. When the GPS device receives an acceptable RSS of the i/s signalbefore entering the deep hole, its timestamp is updated. The mobile GPSdevice 120 compares the last good RSS timestamp value for the other GPSdevices to its current real-time value. If the delta time between thereal time and the timestamp is below a threshold value, then mobile GPSdevice 120 must be potentially close to the i/s coverage area. Thus,mobile GPS device 120 turns on the i/s signal scan since the likelihoodof receiving a sufficient RSS signal has improved, but the i/s signalscan was turned off prior to that point. As a result, the power draindue to futile i/s signal scan attempts is effectively minimized.

Further improvement of the power drain optimization may be realized. Forexample, when mobile GPS device 120 is moving along an approximatelystraight line and encounters several other GPS devices in a row, mobileGPS device 120 may query the time stamp (e.g., last_good_RSS_time)values and determine that their delta time values are consistentlydecreasing. In this case, in anticipation of mobile GPS device 120maintaining the same or similar direction, mobile GPS device 120 mayreduce the delta time threshold to a lower value for turning on the i/ssignal scan. Since mobile GPS device 120 is expecting to encounter asufficient RSS signal (even with a lower delta-time threshold), it canavoid the expenditure of power on some unsuccessful scans with similarRSS detection results.

Further still, the number of devices within the deep hole (i.e., devicedensity) may be used to further improve the power optimization. Whendevice density in the deep hole is low, the power drain resulting fromthe search for GPS devices with Bluetooth or other dedicated short rangecommunication (DRSC) capability may offset the savings via the optimizedi/s signal scan. Thus a device density reasonability threshold ismaintained, such that if the device density is less than this value,then the i/s signal scan power optimization will not be implemented.

The device density threshold may be set based on a number of factorsincluding but not limited to, the power charge budget for the starvingdevice, the actual power charge level of the starving device, theestimated speed and pattern of device movements, and the anticipated i/stimestamp value distribution within the deep hole.

The estimated actual device density value may be determined by dividingthe estimated number or compatible devices in the deep hole by the arealsize of the deep hole. The estimated actual device number can bedetermined by crowd sourcing as described above either by real-timecounting and crowd sourcing the entering and leaving devices or byaveraging historical count values by time of week (TOW), time of day(TOD), etc.

It will be understood, and is appreciated by persons skilled in the art,that one or more functions, modules, units, blocks, processes,sub-processes, or process steps described above may be performed byhardware and/or software. If the process is performed by software, thesoftware may reside in software memory (not shown) in any of the devicesdescribed above. The software in software memory may include an orderedlisting of executable instructions for implementing logical functions(i.e., “logic” that may be implemented either in digital form such asdigital circuitry or source code or in analog form such as analogcircuitry or an analog source such an analog electrical, sound or videosignal), and may selectively be embodied in any computer-readable (orsignal-bearing) medium for use by or in connection with an instructionexecution system, apparatus, or device, such as a computer-based system,processor-containing system, or other system that may selectively fetchthe instructions from the instruction execution system, apparatus, ordevice and execute the instructions. In the context of this document, a“computer-readable medium” and/or “signal-bearing medium” is any meansthat may contain, store, communicate, propagate, or transport theprogram for use by or in connection with the instruction executionsystem, apparatus, or device. The computer readable medium mayselectively be, for example but not limited to, an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system, apparatus,device, or propagation medium. More specific examples, but nonetheless anon-exhaustive list, of computer-readable media would include thefollowing: an electrical connection (electronic) having one or morewires, a portable computer diskette (magnetic), a RAM (electronic), aread-only memory “ROM” (electronic), an erasable programmable read-onlymemory (EPROM or Flash memory) (electronic), an optical fiber (optical),and a portable compact disc read-only memory “CDROM” (optical). Notethat the computer-readable medium may even be paper or another suitablemedium upon which the program is printed, as the program can beelectronically captured, via for instance optical scanning of the paperor other medium, then compiled, interpreted or otherwise processed in asuitable manner if necessary, and then stored in a computer memory.

Although the present invention has been particularly described withreference to the preferred embodiments thereof, it should be readilyapparent to those of ordinary skill in the art that changes andmodifications in the form and details may be made without departing fromthe spirit and scope of the invention. It is intended that the appendedclaims encompass such changes and modifications.

1. A method for updating location data of a mobile Global PositioningSystem (GPS) enabled device comprising: establishing a connection withat least one other mobile GPS enabled device, via a short range wirelessnetwork, based on an age of location data for the at least one othermobile GPS enabled device; and receiving the location data from the atleast one other mobile GPS enabled device.
 2. A method according toclaim 1, wherein the short range wireless network is an ad hoc Bluetoothnetwork.
 3. A method according to claim 1, wherein the location dataincludes ephemeris data.
 4. A method according to claim 3, wherein thelocation data includes time sync data.
 5. A method according to claim 1,further including: comparing an age of location data for the mobile GPSenabled device and the age of location data for the at least one othermobile GPS enabled device; and receiving the location data from the atleast one other mobile GPS enabled device when the age of the locationdata for the at least one other mobile GPS enabled device is less thanthe age of the location data for the mobile GPS enabled device.
 6. Amethod according to claim 5, wherein the location data is received onlywhen a difference between the age of the location data for the at leastone other mobile GPS enabled device and the age of the location data forthe mobile GPS enabled device is above a predetermined threshold value.7. A method according to claim 1, further including detecting a signalstrength for a mobile GPS enabled device.
 8. A method according to claim7, wherein the connection is established with the at least one othermobile GPS enabled device when the signal strength for the mobile GPSenabled device is below a predetermined threshold value.
 9. A methodaccording to claim 7, wherein the signal is a GNSS signal.
 10. A methodaccording to claim 7, wherein the signal is a cellular signal.
 11. Amethod according to claim 7, wherein the signal is a Wi-Fi signal.
 12. Amethod for generating a deep hole map comprising: detecting a signalstrength of at least one mobile Global Positioning System (GPS) device;comparing the detected signal strength of the at least one mobile GPSdevice to a predetermined signal strength threshold value; determining alast known position for the at least one mobile GPS device when thesignal strength of at least one mobile GPS device is below thepredetermined signal strength threshold value; determining a first fixposition for the at least one mobile GPS device when the detected signalstrength returns to a value above the predetermined threshold value; andtransmitting the last known position and the first fix position to acrowd-sourcing server for use in generating the deep hole map.
 13. Amethod of refreshing navigational data comprising: generating a deephole map; determining a position of a mobile Global Positioning System(GPS) device; determining a proximity to a deep hole based on thedetermined position of the mobile GPS device and the generated deep holemap; comparing the determined deep hole proximity to a proximitythreshold; and refreshing the navigational data when the mobile GPSdevice is less than or equal to the to the proximity threshold value.14. A method according to claim 13, wherein the navigational dataincludes ephemeris data.
 15. A method according to claim 13, wherein thenavigational data includes time sync data.